Power detector for mismatched load

ABSTRACT

A method for measuring the forward power output of an amplifier with improved accuracy with a mismatched load based on probing the amplitude of the AC voltage and current in the final amplifier stage. Amplitudes are combined resulting in a composite reading that is affected less by load mismatch. Variations include measuring signal amplitude at two points 90 degrees apart in the transmission medium and measuring the power supply voltage and current of a saturated amplifier.

This is a Divisional of application Ser. No. 10/633,191, filed on Jul.31, 2003 now U.S. Pat. No. 6,924,698, the entire disclosure of which isincorporated herein by reference.

BACKGROUND

As cellular phones have increased in popularity, manufacturers areincluding additional functionality, e.g. photography, email, andaddressbook. These added features are required to fit into a housingthat comfortably fits in a hand. As a result, designers are driven touse the interior space of the housing as efficiently as possible.

One way improve the use of the interior space of a cellular phonehousing is to evaluate the efficiency of existing circuitry, e.g. RFpower detection. FIG. 1 illustrates a prior art example for detecting RFpower. A directional coupler, e.g. a passive structure, is placedbetween the amplifier and the load. The coupler diverts ˜1% of theforward power to the voltage detector, passing most of the power throughto the load. The coupler rejects reflections or reverse power. Thus, thevoltage measurement depends on only the incident forward power, adesirable feature. The coupler, however, introduces power loss and is aphysically large component in the circuit, having a size that dependsupon the operating wavelength.

FIG. 2 illustrates another prior art technique. The voltage detector isdirectly connected to the amplifier output. This circuit has less lossand smaller size than the coupler circuit of FIG. 1, but the detectedvoltage is affected by the reflected power from a mismatched load. Thepower indication will be inaccurate when the load is mismatched.

SUMMARY

A method for measuring the forward power of an amplifier with improvedaccuracy with a mismatched load based on probing the amplitude of the ACvoltage and current in the final amplifier stage. Amplitudes arecombined resulting in a composite reading that is affected less by loadmismatch. The fundamental principle behind the invention is that thedetected voltage and current tend to vary in opposite directions fromthe nominal values as the load deviates from a nominal matched load.This invention provides the advantage of improved measurement accuracywithout the cost or size of a directional coupler. Variations includemeasuring the signal at two points 90 degrees apart in the transmissionmedium and measuring both the power supply voltage and current of asaturated amplifier (i.e. an amplifier that delivers the full supplyvoltage to the load.)

In one embodiment, an amplifier including a current detector, connectsto a voltage detector and a matching circuit. A load interposes thematching circuit and ground. An analyzer receives the outputs of thevoltage detector and current detector. The analyzer scales the outputsof the voltage and current detectors in a ratio such that they would beequal under nominal load conditions, then adds them together. Theanalyzer output reflects the amplitude of the forward power. An optionalgain control may receive the analyzer output and apply it to theamplifier.

In another embodiment, an amplifier has an output connecting to a firstpassive network. A first voltage detector connects to the amplifieroutput. A second passive network serially connects between the firstpassive network and a load. A second voltage detector connects to theoutput of the first passive network. The load is further connected toground. An analyzer receives the outputs of the two voltage detectors.The analyzer multiplies the outputs of the two voltage detectors toreflect the total power. An optional gain control may receive theanalyzer output and apply it to the amplifier.

In another embodiment, an amplifier has an output connecting to amatching network. The matching network connects to a load. The load isfurther connected to ground. A power supply connects to the amplifier. Avoltage detector and current detector monitor power supply draw. Thepower supply draw of the amplifier reflects the AC voltage and currentunder the conditions of class B or C operation and amplifier powersaturation. An analyzer receives the outputs of the voltage detector andcurrent detector. The analyzer scales the outputs of the voltage andcurrent detectors in a ratio such that they would be equal under nominalload conditions, then adds them together. The analyzer output reflectsthe amplitude of the forward power. An optional controller may receivethe analyzer output and apply it to the power supply to control theforward power.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a prior art example with a directional coupler andvoltage detector.

FIG. 2 illustrates a prior art example with a voltage detector.

FIG. 3 illustrates an embodiment of the present invention.

FIG. 4 illustrates a functional block diagram for another embodiment ofthe invention.

FIG. 5 illustrates a functional block diagram for another embodiment ofthe invention.

FIGS. 6A–C illustrate embodiments of the analyzer shown in FIGS. 3, 4,and 5.

DETAILED DESCRIPTION

A method for measuring the forward power of an amplifier with improvedaccuracy with a mismatched load based on probing the amplitude of the ACvoltage and current in the final amplifier stage. Amplitudes arecombined resulting in a composite reading that is affected less by loadmismatch. Variations include measuring signal at two points 90 degreesapart in the transmission medium and controlling the power supply of asaturated amplifier.

FIG. 3 illustrates a functional block diagram 10 of one embodiment ofthe present invention. An amplifier block 12 that includes an amplifier12 a and a current detector 12 b, connected between the power supply 14and ground, connects to a voltage detector 16 and a matching circuit 18.The voltage detector 16 further connects to ground. A load 20 interposesthe matching circuit and ground. An analyzer 22 receives the outputs ofthe voltage detector 16 and current detector 12 b. The analyzer outputreflects either the total power or the amplitude of the power. Anoptional gain controller 24 may receive the analyzer output and apply itto the input of the amplifier 12 a.

FIG. 4 illustrates a functional block diagram 30 for another embodimentof the invention. An amplifier block 32 connects between a power supply34 and ground. The amplifier 32 further has an output connecting to afirst passive network 36. A first voltage detector 38 connects to theamplifier output and ground. A second passive network 40 seriallyconnects between the first passive network 36 and a load 42. A secondvoltage detector 44 connects to the output of the first passive network36. The load 42 is further connected to ground. An analyzer 46 receivesthe outputs of the first voltage detector 38 and the second voltagedetector 44. The analyzer output reflects either the total power or theamplitude of the power. An optional gain controller 48 may receive theanalyzer output and apply it to the input of the amplifier 32.

FIG. 5 illustrates a functional block diagram 50 for another embodimentusing a saturated amplifier. The saturated amplifier 52 has an outputconnecting to a matching network 54. The matching network 54 connects toa load 56. The load 56 is further connected to ground. A power supply 58connects to the amplifier 52. A voltage detector 60 and a currentdetector 62 monitor power supply draw. The power supply draw of theamplifier 52 reflects the AC voltage and current under the conditions ofclass B or C operation and amplifier power saturation. An analyzer 64receives the outputs of the voltage detector 60 and the current detector62. The analyzer 64 scales the outputs of the voltage and currentdetectors 60, 62 in a ratio such that they would be equal under nominalload conditions, then adds them together. The analyzer output reflectsthe amplitude of the forward power. An optional power controller 66 mayreceive the analyzer output and apply it to the power supply to controlthe forward power.

FIGS. 6A–C illustrate embodiments of the analyzer shown in FIGS. 3, 4,and 5.

In FIG. 6A, the output of the current detector 12 b, shown in FIG. 3, orthe first voltage detector 38, shown in FIG. 4, or the output of thecurrent detector 62 of FIG. 5 is scaled. A summation node receives thescaled signal and the voltage. The output of the summation node reflectsthe amplitude of the power.

In FIG. 6B, the output of the voltage detector 16, shown in FIG. 3, orthe second voltage detector 44, shown in FIG. 4, or the voltage detector60 shown in FIG. 5 is scaled. A summation node receives the scaledvoltage signal and the voltage. The output of the summation nodereflects the amplitude of the power.

In FIG. 6C, the outputs of the detectors, e.g. current detector 12 b andvoltage detector 16 in FIG. 3 or first and second voltage detectors 38,44 of FIG. 4, or current detector 62 and voltage detector 60 of FIG. 5are received by a multiplication node. The output of the multiplicationnode reflects the power.

1. A detector comprising: an amplifier, connected between a power supplyand ground, having an amplifier output; a first voltage detector,receiving the amplifier output, and generating a first detected signal;a first passive network, having an input receiving the amplifier output,having a first output; a second passive network, having an inputreceiving the first output, having a second output; a load interposingthe second output and ground; a second voltage detector, receiving thefirst output, generating a second detected signal; and an analyzer,receiving the first and second detected signals, generating an analyzeroutput that reflects a power parameter.
 2. A detector, as defined inclaim 1, further comprising a gain controller receiving the analyzeroutput, electrically connected to an input of the amplifier.
 3. Adetector, as defined in claim 2, the analyzer comprising: amultiplication node, receiving one of the first and second detectedsignals, generating a scaled signal; an arithmetic node, receiving thescaled signal and the other of the first and second detected signals,generating the output that reflects the power parameter.
 4. A detector,as defined in claim 3, wherein the power parameter is total power.
 5. Adetector, as defined in claim 3, wherein the power parameter is theamplitude of total power.
 6. A detector, as defined in claim 3, theanalyzer comprising a multiplication node, receiving the first andsecond detected signals, generating the output that reflects the powerparameter.